Heat radiation shield assembly and sample chamber

Abstract

A heat radiation shield assembly comprising a radiation shield 14 and an opening which allows optical access to a sample (48, fig. 2). The opening is covered by a first window element 34. The first wi

Description

The present invention relates to a heat radiation shield assembly and a sample chamber in particular for a cryostat or cryostation with such a heat radiation shield assembly. For optical manipulation and inspections of samples in vacuum under low temperatures, it is necessary that the vacuum housing containing the vacuum have a window element to allow optical access to the sample. In the vacuum chamber, a sample holder is disposed holding the sample. Therein, the sample holder may be connected to a cooler such as a cold head in order to provide low temperature at the position of the sample holder. The cooler may be configured to provide multiple temperature stages. A 1st stage may provide temperatures ranging from 25K to 60K and a 2nd stage may provide temperatures from 20K to 1.5K or even below. The cooler’s 1st stage may be used to cool a radiation shield or sample support for example, and the cooler’s 2nd stage may be used to cool the sam-ple / device. The cooler may be any cold source that may be in thermal contact with a heat exchanger that is for example cooled by a cryogenic fluid, such as helium or nitrogen. For very low temperatures below 50K and even below 20K the radiation shield needs to be arranged within the vacuum housing in order to prevent any temperature increase of the sample by heat radiation. Radiation shield temperatures can vary, but are typically between 4 and 100K. However, for optical inspection and manipulation of the sample also the radiation shield needs to comprise a window element in order to enable optical access from the outside to the sample. However, for the sake of transparency, window elements are usually made from any kind of glass which exhibits poor heat conductance properties. Thus, an inhomogeneous temperature distribution of the radiation shield window may lead to an increase of heat radiation in the center of the window element of the radiation shield towards the sample. Consequently, there exists a limit regarding the size of the window element of the radiation shield if a certain homogeneity of the temperature distribution across the sample is required. Additionally, heat transfer from the window to the radiation shield is of importance. A large thermal contact resistance between the window and the radiation shield will result in increased window temperature and corresponding heat loads onto the sample. For any window elements of the radiation shield, heat from the window element of the radiation shield cannot be efficiently dissipated and leads to heat radiation causing a temperature increase in particular in the center of the window element of the radiation shield. As used herein a sample refers to any object of interest needed to be cooled to cryogenic temperatures. The problem of poor heat dissipation from the window element of the radiation shield to the sample is amplified if the distance between the sample and the outside shall be small in order to grant optical access by an objective having a limited working distance. It is an object of the present invention to provide a heat radiation shield assembly with improved thermal contact between a radiation shield and a window element. The problem is solved by a heat radiation shield assembly according to claim 1, a sample chamber according to claim 12, and a cryostat according to claim 19. A heat radiation shield assembly in particular for a cryostat according to the present invention comprises a radiation shield to be arranged within a vacuum housing of the cryostat. By the radiation shield heat radiation towards a sample is blocked in order to prevent or reduce heat transfer to the sample to maintain a low and homogeneous temperatures of the sample. Therein, the vacuum housing comprises a vacuum housing opening, wherein a first window element is covering the vacuum housing opening. Thus, by the first window element optical access to the vacuum chamber is provided. Therein, the connection between the vacuum housing and the first window element is provided by a vacuum tight seal. In addition, the radiation shield comprises a radiation shield opening, wherein a first window element is covering the radiation shield opening. Hence, the first window element is functional part of the radiation shield in order to block thermal / heat radiation towards the sample. Therein, connection between the first window element and the radiation shield may or may not be vacuum tight. Since the radiation shield may be fully disposed in a vacuum, a vacuum tight connection between the radiation shield and the first window element may not be necessary. Thus, by the first window element optical inspection and manipulation of the sample inside the cryostat is enabled. As used herein, a window element refers to any substrate, such as fused silica or sapphire, that allows a specific range of electromagnetic wavelengths to pass through. Wavelengths may include the visible spectrum from approximately 400 nanometers up to 700 nanometers or even more broad such as ultraviolet from 330 to 5500 nanometers infrared. According to the present invention, the first window element is in thermal contact with the radiation shield by a spring force. Due to the spring force a tight contact between the first window element and the radiation shield is ensured increasing thermal contact and thermal conductivity between the first window element and the radiation shield. Hence, any heat collected by the first window element due to heat radiation is effectively dissipated via the tight contact with the radiation shield. Sufficient thermal contact between the first window element and the radiation shield can be made by increasing the force between the two. In order to reliably increase the thermal contact the spring force is used. A spring force allows sufficient thermal contact which allows for heat transfer through-out a usable temperature range in cryogenic applications, such as temperatures from 0.1 K to 350K. The spring force remains compliant and provide a sufficient force when other materials in the assembly change dimensions due to thermal contraction / expansion. Consequently, the size of the first window element covering the radiation shield opening can be enlarged. Preferably, the temperature of the radiation shield is below 100K and more preferably below 60K. Preferably, the first window element is made from a glass material or a crystal such as sapphire. Preferably, the diameter of the first window element is between 5mm and 100mm. In particular, the diameter of the first window element is larger than the diameter of a sample in order to allow full optical access. Sample sizes can range from 0.1mm diameter to greater than 76.2mm diameters. For a 3 inch wafer for example, the first window element would be larger than 76.2mm in diameter to allow full optical access. Preferably, the thickness of the first window element is between 0.2mm and 20mm, preferably between 0.2mm and 5mm and more preferably between 0.2mm and 2mm. Preferably, the first window element is releasably connected to the radiation shield. Hence, the first window element can be replaced easily and can be adapted to the respective manipulation and / or inspection methods to be applied to the sample. Preferably, thermal grease may be applied between the first window element and the radiation shield to increase thermal conductance from the first window element to the radiation shield. Preferably, the spring force is provided by a resilient element or spring and in particular by a wavespring. Therein, in particular the wavespring surrounds the radiation shield opening in order to apply the spring force to the first window element. Preferably, the spring force is between 40N / cm2 and 100N / cm2 and in particular between 50N / cm2 and 80N / cm2. It has been found by the inventors of the present invention, that the specific range for the spring force applied to the first window element is sufficient in order to guarantee sufficient thermal contact between the radiation shield and the first window element. On the other hand, damage of the first window element can be avoided. Preferably, the spring is made from stainless steel providing a reliable spring force to the first window element, but other types of spring material may be used such as carbon steel, beryllium copper, Inconel, or the like. Preferably, the radiation shield comprises a recess, wherein the resilient element or spring is arranged in the recess. Additionally, the first window element may also be arranged in the recess while the first window element is clamped by the resilient element or spring between the shoulders of the recess. Preferably, a pressure distribution element is arranged between the resilient element or spring and the first window element. By the pressure distribution element, a pressure of the resilient element or spring is distributed and more homogenously applied to the first window element. Therein, the pressures distribution element may provide a full surface contact to the first window element in order to apply the pressure generated by the resilient element or spring homogenously to the first window element. Preferably, the pressure distribution element is made from aluminum, copper, titanium, or stainless steel. Preferably, the radiation shield comprises a first radiation shield element forming the radiation shield opening and a second radiation shield element. Therein, the first radiation shield element and the second radiation shield element may be connected by bolts or clamps or the like. In particular, the recess is formed by the first radiation shield element and an abutment surface or shoulder of the recess is formed by the second radiation shield element or the other way around. Hence, for assembly of the first window element, the first window element can be arranged in the first radiation shield element closing the radiation shield opening. Subsequently, the optional pressure distribution element can be inserted followed by the resilient element or spring. In a last step, the second radiation shield element is connected to the first radiation shield element such that the first window element and the spring or resilient element are clamped between the first radiation shield element and the second radiation shield element. Alternatively, the order of the first window element and the spring or resilient element can be exchanged in that first the spring or resilient element is inserted, followed by the optional pressure distribution element and the first window element. Preferably, the radiation shield comprises a rim and the first window element abuts against the rim. Using a thin rim on the radiation shield allows for optical access to larger samples within short distance. In particular, the rim is arranged in a direction away from the spring or resilient element such that by the spring force the first window element is pressed against the rim. Hence, the position of the first window element is limited by the rim and clamped by the resilient element or spring due to the spring force against the rim of the radiation shield. Contact of the first window element with the rim ensures and improves thermal contact between the first window element and the radiation shield. Thermal grease or indium foil may be used to improve the thermal contact between the first window element and the radiation shield, but thermal grease and indium foil are less critical for the present invention. In particular, not needing thermal grease in ultra-high vacuum and extreme high vacuum levels might be beneficial. Preferably, the radiation shield comprises a rim and the spring or resilient element abuts against the rim. Hence, the first window element is arranged opposite to the rim relative to the spring or resilient element. In other words, the spring or resilient element is supported by the rim and clamping the first window element against the shoulder or abutment surface of the second radiation shield element which eliminates a thermal joint to contend with. This will allow for colder temperatures to be achieved without an intermediate thermal joint between the first radiation shield element and the second radiation shield element. In particular, the rim is arranged in a direction away from the first window element such that by the spring force the first window element is pressed against the shoulder or abutment surface. Preferably, the rim is integrally formed with the radiation shield, i.e. one of the radiation shield elements and preferably with the first radiation shield element. Preferably, the contact surface area between the rim and the first window element or the abutment surface, respectively, is sufficiently sized to prevent damage to the first window element or rim. Areas are dependent on the size of the first window element and may range from 0.5cm2 to more than 20cm2. With increasing contact surface, thermal contact between the rim / abutment surface and the first window element is increased allowing improved heat dissipation from the first window element to the radiation shield. Additionally increased contact force allows for improved heat dissipation from the first window element to the radiation shield. Preferably, the rim extends radially inward by between 1mm to 12mm, preferably by between 5mm to 10mm and more preferably by between 7mm and 9mm, and may be dependent on the contact area and force desired which is dependent on size of the first window element. In particular, the rim extends radially inward by more than 1mm, preferably by more than 5mm and more preferably by more than 7mm. The design of the first window element, radiation shield, spring / resilient element, and the optional pressure distribution element allows for vertical and radial contraction and expansion of each individual component relative to the adjacent components which prevents damage and also ensures the spring force and thermal contact remains sufficient. Consequently, this allows for the radiation shield to contract more than the first window element and does not cause damage to the first window element. In another aspect of the present invention a sample chamber for a cryostat is provided. The sample chamber comprises a vacuum housing defining a vacuum chamber that is connectable to a vacuum pump and may contain a vacuum. In particular, the vacuum housing is vacuum tight and may be made from aluminum. A sample holder is arranged within the vacuum housing. The sample holder is connectable to a cooler in order to provide a low temperature to the sample holder. A sample can be arranged on the sample holder and cooled to low temperatures. Further, a heat radiation shield assembly as described before is arranged within the vacuum housing and at least partially surrounding the sample holder / sample. Preferably, the vacuum housing comprises a vacuum housing opening, wherein a second window element is covering the vacuum housing opening. Thus, by the second window element optical access to the vacuum chamber is provided. The connection between the vacuum housing and the second window element is provided by a vacuum tight seal. Therein, the first window element and the second window element are arranged above the sample holder to grant optical access to a sample on the sample holder. Therein, “above” refers to the direction of the sample holder and can be in the horizontal direction, the vertical direction or any intermediate direction. “Above” merely refers to the direction corresponding to the direction for optical access from the outside to the sample on the sample holder. In particular, the first window element and the second window element are arranged along an axis which is perpendicular to a surface of the sample holder configured to receive the sample. In particular, the first window element and the second window element are concentrically arranged relative to each other. Alternatively or additionally the first window element may be arranged concentrically to the sample holder and / or the second window element is concentrically arranged relative to the sample holder. Preferably, the second window element is releasably connected to the vacuum housing. Hence, the second window element can be replaced easily and can be adapted to the respective manipulation and / or inspection methods to be applied to the sample. Preferably, the sample holder has a temperature of between 0.1 K to 350K and preferably below 20K and more preferably below 4K. Preferably, a temperature difference across the sample holder is below 5K, more preferably below 1K and most preferably below 0.1 K. Hence, the heat induced to the sample by heat radiation from the first window element is kept to a minimum, which is achieved by an improved contact between the first window element and the radiation shield due to the spring force. Preferably, the second window element is made from a glass material or a crystal such as sapphire. In particular, the first window element and the second window element are made from the same material, but could be different depending on the optical and vacuum requirements. Since optical inspection and / or manipulation of the sample in the sample chamber is desired, transmission / absorption of the first window element and the second window element needs to be aligned and the least partially overlapping with each other in order to grant optical access to the sample. Preferably, the distance from a top surface of the second window element to a top surface of the sample holder is 50mm or less and preferably 12mm or less. This allows optical inspection and manipulation of the sample located on the sample holder by an objective having a limited working distance. Preferably, the vacuum housing has a recess or step. In particular, the recess is arranged around the vacuum housing opening and is configured to receive the second window element. In particular, the recess is open from the outside of the sample chamber, i. e. a side opposite to the sample holder. Thus, the second window element can be inserted into the recess from the outside. Preferably, an O-ring is arranged between the second window element and the vacuum housing in order to provide a vacuum tight seal between the second window element and the vacuum housing. Preferably, the recess is at least partially covered by a retaining element, wherein the second window element is arranged between the recess and the retaining element. Thus, by the retaining element the second window element is secured in the recess. Preferably, a distance from the recess or step to the lower side of the retaining element is larger than the second window element, i.e. the thickness of the second window element. Consequently, the second window element is fixed by the retaining element during times when the cryostation is not under vacuum. Once vacuum is applied, the O-ring is fully compressed due to the vacuum force and the retaining element is no longer touching the second window element. In particular, the retaining element may be connected to the vacuum chamber by bolts. Clamping of the second window between two rigid elements may cause the second window element to break due to stress. Instead, the second window element is sucked in to the recess by the vacuum in the vacuum chamber and pressed by the vacuum against any seal element, i. e. an O-ring. Preferably, the sample holders are made from copper providing a good thermal conductivity. Preferably, the diameter of the second window element is between 5mm and 100mm. In particular, the diameter of the first window element and / or the second window element is larger than the diameter of the sample in order to allow full optical access. Sample sizes can range from 0.1mm diameter to greater than 76.2mm diameters. For a 3 inch wafer for example, the first window element and second window element would be larger than 76.2mm in diameter to allow full optical access. Preferably, the thickness of the second window element is between 1mm and 30mm, more preferably between 1mm and 15mm and most preferably between 2mm and 6mm. Preferably, a gap is present between an upper side of the first window element and a lower side of the second window element. Therein again, the upper side and lower side refer in a direction perpendicular to a surface of the sample holder. In other words, the upper side of the first window element and the lower side of the second window element refer to opposing surfaces of the respective window elements. In particular, the gap between the first window element and the second window element is smaller than 5mm, preferably smaller than 1mm. Due to the improved thermal contact geometry between the first window element and the radiation shield, the gap between the first window element and the second window element can be kept small in order to achieve a small distance between the sample and the outside of the sample chamber. Preferably, the sample chamber comprises more than one heat radiation assembly, wherein the radiation shields are nested. Furthermore, temperatures of the individual radiation shield may decrease from the vacuum housing towards the sample holder. In another aspect of the present invention a cryostat or cryostation is provided comprising a sample chamber as described before and a cooler thermally connected to the sample holder. In particular, the cooler is provided by a cold head able to provide temperatures on the first stage between 25 and 60K and for the second stage temperatures from 1.5K to 20K or below. Preferably the radiation shield is connected to the cooler to maintain the temperature of the radiation shield. In particular, the radiation shield is connected to the first stage of the cooler. Preferably, a vacuum pump is connected to the vacuum housing in order to maintain a vacuum in the vacuum chamber. Preferably, the temperature gradient across the sample holder is less than 10K and more preferably less than 0.1 K. Thus, by the present invention a homogeneous temperature distribution across the sample holder is provided. With this invention, the second window element is approximately 44K colder than the ambient temperature. In the following the present invention is described in more detail with reference to the accompanying figures. The figures show: Figure 1 a sectional view of a sample chamber according to the present invention, Figure 2 a detailed view of the sample chamber according to figure 1, Figure 3 a detailed view of the window elements in a sideview, and Figure 4 another embodiment of the heat radiation shield. The sample chamber 10 according to the present invention comprises a vacuum housing 12 defining a vacuum chamber 13. Therein, the vacuum chamber 12 may be built by a first vacuum housing element 18 and a second vacuum housing element 20 connected in a vacuum tight manner. The vacuum chamber 13 may be connected to a vacuum pump (not shown) in order to provide a vacuum inside the vacuum chamber 13. A sample holder 16 is arranged within the vacuum housing 12 and in the vacuum chamber 13. The sample holder 16 comprises an upper surface 44 (see Fig. 3), wherein a sample 48 may be arranged on the upper surface 44 of the sample holder 16 and may be clampingly fixed. The sample holder 16 is connectable to a cooler in order to be cooled down to low temperature preferably below 20K and more preferably below 4K. At lower temperatures such as 4K and below, this invention becomes more important since the cooling power available for cooling the sample diminishes. In particular, the cooler is provided by cold head or a liquid helium cryostat. The vacuum housing 12 comprises a vacuum housing opening 28, wherein a second window element 32 is arranged in the vacuum housing opening 28. In particular, the second window element 32 is arranged above the upper surface 44 of the sample holder 16 and in particular above the sample 48 in order to allow optical inspection and manipulation of the sample 48 from the outside of the sample chamber 10. A radiation shield 14 is arranged within the vacuum chamber 13 and partially and preferably completely surrounds the sample holder 16. Therein, by the radiation shield 14, heat radiation transferred from the vacuum housing 12 or the outside towards the sample holder 16 or the sample 48 is eliminated or reduced. In particular, the radiation shield 14 is kept at a low temperature, preferably between 20K and 100K. In particular, the temperature of the radiation shield 14 is between the temperature of the vacuum housing 12 (in general room temperature) and the temperature of the sample holder 16. For an use case of a 2-stage cold head, the radiation shield 14 is preferably thermally connected to 1st stage of cold head and the sample 48 is thermally connected to 2nd stage of cold head. The radiation shield 14 comprises a radiation shield opening, wherein a first window element 34 is arranged in the radiation shield opening, i. e. covers the radiation shield opening. In particular, the first window element is arranged above the upper surface 44 of the sample holder 16. In particular, the first window element 34 and the second window element 32 are arranged concentrically and in correspondence with the sample holder 16 in order to allow optical inspection and manipulation of the sample 48 on the upper surface 44 of the sample holder 16. Therein, the first window element 34 and the second window element 32 are made from a transparent material, i. e. being transparent at a specific wavelength necessary for inspection and / or manipulation of the waver sample 48. In particular, the transmission of the first window element 34 at least partially overlaps with the transmission of the second window element 32 in order to allow optical access to the sample 48. In accordance with the present invention the first window element 34 and the second window element 32 are releasably connected to either the heat radiation shield 14 and / or the vacuum housing 12, respectively, in order to be replaceable and adaptable to the specific application of the sample chamber 10. Hence, for different purposes, different window elements 32, 34 can be installed. The first window element 34 and / or the second window element 32 may be fused silica or any other glass, or a crystal such as a sapphire. The second window element 32 comprises an upper surface 30 and a lower surface 40, wherein the upper surface 30 is exposed to ambient pressure outside the vacuum chamber 13. The first window element 34 comprises an upper surface 38 opposite to the lower surface 40 of the second window element, and a lower surface 44 being opposite to the upper surface 44 of the sample holder 16. Therein, between the first window element 34 and the second window element 32 a small gap exists. In particular the gap has a size of below 5mm. Here and in the following it is referred to "upper" and "lower", wherein these relative terms are used to describe the structure as pictured in the Figures. Therein, the main direction is indicated by arrow 15 in Figure 3 and is used to indicate a direction starting from the sample holder 16 towards the second window element 32, wherein, the term "upper", "lower" shall not be construed as limiting and consequently the sample chamber shall be used in any orientation. In particular, the upper surface 44 of the sample holder does not need to be horizontal or the main direction 15 being substantially perpendicular to the upper surface 44 of the sample holder 16 does not need to be a vertical direction. Hence, the sample chamber according to the present invention can be used in any orientation and are not limited to the indicated orientation of the Figures. Although indicated in the Figures that the first window element 34 is parallel to the second window element 32 and in particular the upper surface 30 of the second window element 32 and / or the lower surface 40 of the second window element 32 are parallel to the upper surface 38 of the first window element 34, other configurations may also exist and encompassed by the present invention. Thus, the first window element 34 and the second window element 32 may be oblique to each other or at least one of the surfaces of the first window element 34 and / or the second window element 32 may be oblique to another surface. Thereby reflection may be reduced which would otherwise obstruct optical manipulation and inspection of the sample 48. In order to increase thermal contact between the heat shield 14 and the first window element 34, the heat shield 14 comprises a rim 60 extending in a radial direction. In particular, the rim has a width D, i. e. extends in a radial direction by between 0.5mm to 12mm. Hence, the rim 60 is in direct and close contact with the upper surface 38 of the first window element 34. Consequently, heat can be efficiently transferred from the first window element 34 towards the radiation shield 14. Therefore, the first window element 34 is pushed against the rim 60 by a spring 52 which is in the embodiments of the Figures formed as wavespring. By the rim 60 an area of a contact surface between the upper surface 38 of the first window element 34 and the radiation shield 14 is preferably more than 0.5cm2 up to 20cm2, but could be more or less depending on the size of the second window element. By the spring force, the first window element 34 is pushed against the rim 60 with a spring force of between 40N / cm2 and 100N / cm2 and preferably between 50N / cm2 and 75N / cm2. Although in the Figures the spring force is provided by a wavespring 52, other spring elements can be utilized in order to provide the spring force such as resilient elements or other kinds of springs. Between the spring 52 and the first window element 34 a pressure distribution element 54 is arranged. Therein, the heat radiation shield 14 may comprise a first heat radiation element 22 and a second heat radiation element 24. By the radiation shield 14 a recess 50 is provided, wherein the wavespring 52, the pressure distribution element 54 and the first window element 34 are arranged in the recess 50. Therein, the recess is limited at the upper end by the rim 60 which may be connected to and preferably integrally formed with the first radiation shield element 22. Opposite to the rim 60 the recess 50 is limited by a shoulder or step 51 provided by the second radiation shield element 24 which serves as an abutment surface of the recess. Hence, for assembly, the first radiation shield element 22 is provided. Subsequently, the first window element 34 is inserted into the recess 50 thereby covering the radiation shield opening provided by the first radiation shield element 22. Subsequently, a pressure distribution element 54 is arranged (if implemented) in the recess 50 followed by the wavespring 52. The second radiation shield element 24 is connected to the first radiation shield element 22 for example by bolts, screws or the like, thereby allowing the wavespring 52 to apply the spring force to the first window element 34 and ensure a tight contact between the rim 60 of the radiation shield 14 and the first window element 34. The geometry allows to achieve a certain force, wherein too much force would result in failure, and too little force would not provide sufficient thermal contact. The geometry of the present invention allows for an easy method to achieve the right force. Consequently, heat induced into the second window element 34 for example by heat radiation from the vacuum housing 12 can be efficiently dissipated via the radiation shield 14 and heat radiation from the first window element 34 towards the sample holder 16 is minimized. In another embodiment shown in Fig. 4, the order of the wavespring 52 and first window element 34 is reversed such that the rim 60 is in contact with the wavespring 52 pressing the first window element 34 against the shoulder or step 51 of the second radiation shield element 24. The vacuum housing 12 comprises a recess or step 62, wherein the second window element 32 is inserted into the recess or step 62. In particular, the second window element 32 is inserted into the recess 62 from the outside. An O-ring or seal element 64 ensures a vacuum tight connection between the second window element 32 and the vacuum housing 12. Other sealing materials could be a conflat metal gasket, indium, epoxy, or the like. A retaining element 66 is attached to an upper surface 26 of the vacuum housing 12 and is closing the recess 62 in order to hold the second window element 32 in the recess 62. Therein, the second window element 32 is not rigidly fixed by the retaining element 66, but retained in the recess 62, when the cryostation is not under vacuum. In particular, a distance W between the step or recess 62 of the vacuum housing 12 and a lower surface of the retaining element 66 is larger than a thickness of the second window element 32 in the main direction 15. Consequently, no clamping force is directly applied by the retaining element 66 through the second window element 32, and directly onto the vacuum housing 12. The O-ring 64 allows for compliance to prevent cracks or braking of the second window element 32 in particular due to stress from tightening the bolts on the retaining element 66. During operation of the cryostation, once a strong enough vacuum is created inside the vacuum chamber 13, second window element 32 compresses O-ring 64 and bottoms out onto the vacuum housing 12 to create a sufficient repeatable vacuum chamber seal. Thus, the second window element 32 is hold in place by the vacuum within the vacuum chamber 13 and pressed against the seal element 64. However, in order to replace the second window element 32, the retaining element 66 is removed from the vacuum housing 12, the second window element 32 is replaced by another second window element and the retaining element is connected to the upper surface 26 of the vacuum housing 12. 5 Hence, by the present invention, a heat radiation shield assembly and a sample chamber is provided, wherein an improved thermal contact between the first window element 34 and the radiation shield 14 is provided. Efficient heat dissipation from the first window element 34 through the radiation shield 14 allows increase of size of the first window element 34 10 without an overlarge heat gradient on the upper surface 44 of the sample holder 16. In particular, the diameter of the first window element 34 may be above 76mm. Due to the improved thermal contact between the first window element 34 and the radiation shield 14, a temperature gradient across the sample 48, i. e. across the upper surface 44 of the sample holder 16, is below 10K and more preferably below 0.1K. At the same time the first 15 window element and the second window element can be replaced and adapted to the respective application. Reference list 10 sample chamber 12 vacuum housing 13 vacuum chamber 14 radiation shield 15 main direction 16 sample holder 18 first vacuum housing element 20 second vacuum housing element 22 first radiation shield element 24 second radiation shield element 26 upper surface 28 vacuum housing opening 30 upper surface 32 second window element 34 first window element 38 upper surface 40 lower surface 42 lower surface 44 upper surface 48 sample 50 recess 51 step 52 wavespring 54 pressure distribution element 60 rim 62 recess 64 sealing element 66 retaining element

Claims

1. Heat radiation shield assembly in particular for a cryostat, comprising:a radiation shield;wherein the radiation shield comprises a radiation shield opening to allow optical access to a sample in the cryostat, wherein a first window element is covering the radiation shield opening;wherein the first window element is in thermal contact with the radiation shield by a spring force.

2. Heat radiation shield assembly according to claim 1, wherein the first window element is releasably connected to the radiation shield.

3. Heat radiation shield assembly according to claim 1 or 2, wherein the spring force is provided by a resilient element or a spring and in particular by a wavespring.

4. Heat radiation shield assembly according to claim 3, wherein the spring force is between 40N / cm2 and 100N / cm2.

5. Heat radiation shield assembly according to claim 3 or 4, wherein the radiation shield comprises a recess, wherein the resilient element or spring is arranged in the recess.

6. Heat radiation shield assembly according to claim 5, wherein the first window element is arranged in the recess.

7. Heat radiation shield assembly according to any of claims 3 to 6, wherein a pressure distribution element is arranged between the resilient element or spring and the first window element.

8. Heat radiation shield assembly according to any of claims 1 to 7, wherein the radiation shield comprises a rim and the first window element abuts against the rim.

9. Heat radiation shield assembly according to claim 8, wherein the contact surface between the rim and the first window element is more than 0.5cm2, preferably more than 20cm2.

10. Heat radiation shield assembly according to claim 8 or 9, wherein the rim extends radially inward by between 1mm to 12mm, preferably by 5mm to 10mm and more preferably by between 7mm and 9mm.

11. Heat radiation shield assembly according to any of claims 1 to 10, wherein the radiation shield comprises a first radiation shield element forming the radiation shield opening and a second radiation shield element, wherein preferably the recess is formed by the first radiation shield element and an abutment surface of the recess is formed by the second radiation shield element.

12. Sample chamber for a cryostat, comprising:a vacuum housing connectable to a vacuum pump;a sample holder arranged within the vacuum housing and connectable to a cooler; anda heat radiation shield assembly according to any of claims 1 to 11 arranged within the vacuum housing, wherein the radiation shield at least partially surrounding the sample holder.

13. Sample chamber according to claim 12, wherein the vacuum housing comprises a vacuum housing opening, wherein a second window element is covering the vacuum housing opening, wherein the first window element and second window element are arranged above the sample holder to grant optical access to a sample on the sample holder.

14. Sample chamber according to claim 12 or 13, wherein the distance from a top surface of the second window element to a surface of the sample holder is 50mm or less and preferably 12mm or less.

15. Sample chamber according to any of claims 12 to 14, wherein the second window element is releasably connected to the vacuum housing.

16. Sample chamber according to any of claims 12 to 15, wherein the vacuum housing has a recess to receive the second window element.

17. Sample chamber according to claim 16, wherein the recess is at least partially covered by a retaining element, wherein the second window element is arranged between the recess and the retaining element.

18. Sample chamber according to claim 16 or 17, wherein a distance from the recess to the lower side of the retaining element is larger than a width of the second window element.

19. Cryostat comprising a sample chamber according to any of claims 12 to 18 and a cooler thermally connected to the sample holder.IntellectualPropertyOfficeApplication GB2501221.2Search report under Section 17 of the Patents Act 1977Date search completed: 28 July 2025Claims searched: 1-19International classificationSubclass and subgroup Valid from F25D27 / 00 01 / 01 / 2006 G21f7 / 03 01 / 01 / 2006Field of searchWorldwide search of patent documents classified in the following areas of the IPC:G21F, F25DDatabases used in the preparation of this search report:SEARCH-PATENTDocuments considered to be relevantPatent literatureCategory Relevant Document of relevanceclaimsA - US 2010 / 0050661 A1SNOW, See paragraphs [0078]-[0080] and fig 5.A - US 2014 / 0123684 A1 TOFT, See paragraph [0023] and fig 3 A - US 313947 A WEECH, See fig 1 and column 5 lines 27-45 A - JP H08166331 A YAMAMOTO, See figure 1 and WPI abstract accession no. 1996-351158 A - US 318830 A COWANS, See figure 2 and 3column 3 lines 31-46 A - US 2021 / 0310720 A1 GIVENS, See figure 3 and paragraph [0026] Non-patent literature Category Relevant claims Document of relevanceCategoriesLetter or DescriptionsymbolX Document indicating lack of novelty or inventive step.Y Document indicating lack of inventive step, if combined with anotherdocument of the same category.& Member of the same patent family.Letter or symbol Description A Document indicating technological background. P Document published on or after the priority date but before the fling date of the present application. E Earlier application published on or after the filing date of the present application.

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